1. Field of the Invention
The invention relates to a method and an apparatus for monitoring a plant having several functional units, such as a production plant.
2. Description of the Prior Art
Hitherto in the case of control devices parallel emergency shut-off wiring systems have been used, which are implemented in relay technology. Problems have arisen in connection with the safety with programming hand-operated equipment (operating units), whose flexible connecting cables are exposed to many actions, so that it is not possible to reliably exclude short-circuiting between emergency shut-off lines. The necessary two-channel or duct nature also makes the cable stiff, thick and heavy. Parallel-wired safety circuits are designed in an application-specific manner and offer no flexibility. Functional changes are only possible through reconstruction. Emergency-off loops and operator protection loops are admittedly extendable, but do not offer the possibility of a diagnosis, if a signal generator is opened in the safety circuit of a machine control. In addition, it is difficult to monitor and maintain such safety devices and the large number of participating contacts of the safety logic has a negative influence on operating safety and reliability.
Therefore the problem solved by the invention is to provide a method and an apparatus, by means of which in a simple, easily monitored manner it is possible to bring about an increase in safety in a complex plant, of the type described hereinbefore.
In a plant, such as a production plant, on which the invention is based, it can be a question of one or more associated machines, such as e.g. robots. A machine or robot comprises several different functional units, such as the power module of a control unit and an operating unit. In such a plant, several such machines can cooperate and be interlinked with the functional units. In addition, peripherals can be present, such as rails, on which are moved the machines, such as robots, or a portal, which moves the machines or robots along a xe2x80x9cworkpiecexe2x80x9d to be machined, such as a ship.
According to the invention the problem of the prior art is solved by a method of the aforementioned type, wherein each functional unit is individually checked or monitored by its own redundant, two-channel safety devices, the safety devices continuously inform one another about their inspection state and in the case of a malfunction of at least one functional unit or safety device, a safety-relevant actuator is operated. In a device according to the invention with each functional unit is in each case associated its own redundant, two-channel safety device and the safety devices are so interconnected that in the case of a malfunction of at least one functional unit or safety device, they operate at least one safety-relevant actuator.
The invention provides a distributed safety logic, in which each safety device has all the necessary safety functions, which permits a high quality diagnosis. The safety devices are connected or communicate with one another, so that they can monitor one another and a safety device is able to detect the failure of another such device and can therefore emit a safety-relevant signal for operating an actuator.
According to a first, preferred embodiment, the safety devices have a controller core and an interface wiring. As a result the safety devices can be constructed in a very simple and easily monitorable manner.
According to a preferred development, the safety devices serially communicate or are interconnected with one another. As a result of the serial connection, parallel wiring is rendered superfluous. Necessary cable cross-sections can be reduced, which is in particular very advantageous for portable equipment, such as operating or programming hand-operated equipment.
According to another preferred embodiment, the safety devices communicate with one another by means of a ring protocol or the safety devices are interconnected in a ring. Thus, the complete safety mechanism can be randomly extended in a simple manner. If e.g. the plant receives further functional units, the associated safety devices can be readily, easily integrated. This ensures a simple, easily monitorable adaptability to different plants. Addressing can take place physically by placing in the bus. A reliable reaction is immediately attainable on extending the ring protocol.
It is possible for each safety device to have at least one microprocessor. According to a preferred further development, each safety device has at least two microprocessors. According to other preferred developments, each safety device has diagnostic inputs and in particular the diagnostic inputs are synchronized with test switching cycles of the safety-relevant inputs or the safety devices continuously perform a diagnosis of the functional units associated with them and consequently the plant. This makes it possible to localize signal generators, which have emitted a safety-relevant signal. It is also possible to carry out a permanent monitoring and diagnosis of the complete plant.
According to another preferred development, microprocessors contained in the safety devices cyclically check their processor image and the result calculated therefrom and/or the content of memories and in particular the correct connection and function of the signal inputs and signal generators is checked. Because of the redundant design of the safety devices in the aforementioned manner, the microprocessors can cyclically check one another and the surrounding hardware and simultaneously the program which is running can be checked for consistency. The content comparison of the processors takes place over the complete ring in the case of a ring protocol.
According to further developments of the apparatus according to the invention, each safety device has at least one safety-relevant output and/or each safety device has several safety-relevant inputs.
The complete safety structure becomes simple and very inexpensive if, according to a further development, the safety devices are constructed identically and preferably the basic software integrated into the identical safety devices is also identical and adaptations take place solely by means of software components or switches.
The method and apparatus according to the invention offer significant advantages. The ring structure of the complete monitoring device is only closed when all the functional units and their associated, individual safety devices are operating. Communication is interrupted, if a safety device indicates a malfunction. When such a lasting fault occurs, a disconnection takes place and the complete system passes into a safe state.
Further advantages result from the decentralized structure achieved by the invention which, as stated, is flexibly extendible, but still achieves reliable operating safety with limited space demands and costs. Wiring costs are minimized as a result of the inventive solution and diagnostic possibilities are improved. The safety devices according to the invention can be easily integrated into existing equipment.